APOD: The Hubble Extreme Deep Field (2012 Oct 14)

[APOD Robot]

The Hubble Extreme Deep Field

Explanation: What did the first galaxies look like? To help answer this question, the Hubble Space Telescope has just finished taking the eXtreme Deep Field (XDF), the deepest image of the universe ever taken in visible light. Pictured above, the XDF shows a sampling of some of the oldest galaxies ever seen, galaxies that formed just after the dark ages, 13 billion years ago, when the universe was only a few percent of its present age. The Hubble Space Telescope's ACS camera and the infrared channel of the WFPC3 camera took the image. Combining efforts spread over 10 years, the XDF is more sensitive, in some colors, than the original Hubble Deep Field (HDF), the Hubble Ultra Deep Field (HUDF) completed in 2004, and the HUDF Infrared completed in 2009. Astronomers the world over will likely study the XDF for years to come to better understand how stars and galaxies formed in the early universe.

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[bystander]

http://asterisk.apod.com/viewtopic.php?t=29624

[Ann]

An image like this one is hugely interesting, and it is very good that the Hubble telescope is being used for purposes like this.

I found this part of the caption a little confusing:

the Hubble Space Telescope has just finished taking the eXtreme Deep Field (XDF), the deepest image of the universe ever taken in visible light

So what does "visible light" mean here? You can find out what filters were used for this image here. The filters were F105W (Y), F125W (J), and F160W (H).

As you can see if you follow the links, the Y, J and H filters are all infrared filters. So you might think that the filters don't actually track visible light. But because the galaxies are so distant, the photons detected by these filters were originally emitted as visible light and have been redshifted into the infrared part of the spectrum by the expansion of the universe.

Even so, I think it is quite difficult to "read" the colors of the galaxies. All of the largest spirals look blue, but the largest of them all at 9 o'clock is far from the bluest of the lot. At the same time, its somewhat ragged shape suggests that the galaxy is nevertheless quite full of hot young stars. So why is its blue color diluted with yellow? Could it be that this is a fairly mature galaxy, so that it has an established yellow bulge just like modern spiral galaxies? To me, this galaxy resembles the large Virgo spiral galaxy M61.

Speaking of blue galaxies, there are three very blue and quite large galaxies in the upper left quadrant of the picture. Could they be strongly dominated by star formation, like modern-day NGC 3310?

There are, on the other hand, tiny blue dots and squiggles scattered everywhere all over the picture. They are likely very early and small starforming dwarf galaxies.

A few very red spirals or disk galaxies interest me. At 7 o'clock is a very red smallish spiral which resembles spiral galaxies M95 or M96. Both M95 and M96 are mature spiral galaxies dominated by old yellow stars, and it is fascinating that there might be counterparts to them that are ten billion years old or so.

A very red edge-on spiral or disk galaxy is seen at 1 o'clock. Could its red color be due to copious amounts of dust?

This is indeed a fascinating picture. I wonder how professional astronomers interpret the colors and shapes of the galaxies we see here.

Ann

[bystander]

So what does "visible light" mean here? You can find out what filters were used for this image here. The filters were F105W (Y), F125W (J), and F160W (H).

Those are the filters used for the HUDF IR (2009). While they were also used here, they are all combined into red. Blue and green come from five other filters, four of which were also used in the HUDF (2004). The information can be found here for the XDF (2012).

[Chris Peterson]

I found this part of the caption a little confusing:

the Hubble Space Telescope has just finished taking the eXtreme Deep Field (XDF), the deepest image of the universe ever taken in visible light

So what does "visible light" mean here? You can find out what filters were used for this image here. The filters were F105W (Y), F125W (J), and F160W (H).

As you can see if you follow the links, the Y, J and H filters are all infrared filters. So you might think that the filters don't actually track visible light. But because the galaxies are so distant, the photons detected by these filters were originally emitted as visible light and have been redshifted into the infrared part of the spectrum by the expansion of the universe.

I don't think the caption was based on any assumptions about redshift. In fact, astronomers commonly call light out to about 1.5 um "visible" because from a physical standpoint it behaves the same as light from there up to near UV- it is imaged by conventional optics and recorded by conventional silicon detectors. Terminology tends to change with the optical and detection technology required for any particular wavelength range.

[starchaser]

This image compares the angular size of the XDF field to the angular size of the full Moon. The XDF is a very small fraction of sky area, but it provides a "core sample" of the heavens by penetrating deep into space over a sightline of over 13 billion light-years. Several thousand galaxies are contained within this small field of view. At an angular diameter of one-half degree, the Moon spans an area of sky only one-half the width of a finger held at arm's length.

Source: http://hubblesite.org/newscenter/archiv ... 7/image/c/

Truly amazing, and gets things into perspective about the vastness of our Universe!

[Boomer12k]

There is a much more informative picture of what they are really talking about...it is not so much the "foreground" galaxies...this page has a cut out view...

You can't even see that spot in the magnified APOD view...

http://www.news.com.au/technology/sci-t ... 5995240242


:---[===] *

[Ann]

So what does "visible light" mean here? You can find out what filters were used for this image here. The filters were F105W (Y), F125W (J), and F160W (H).

Those are the filters used for the HUDF IR (2009). While they were also used here, they are all combined into red. Blue and green come from five other filters, four of which were also used in the HUDF (2004). The information can be found here for the XDF (2012).

Thanks for the clarification, bystander. Thanks to Chris, too.

Ann

[billbat32]

If we sent the Hubble telescope back in time and distance to the point where it has now collated these pictures, what would it see?

I believe exactly the same. Pictures from billions of years ago.

I think that the driving force of everything is gravity and is caused by successive big bangs driven by over-full black holes releasing the matter back out into space as we percieve it. The universe must be ongoing or we would not be here.

We have only been literate in science for 100 years +. When we find out that the speed of light is not the fastest thing around then we may make some effort at off-world communication and get a better answer to our questions.

We are still at steam train level in space/science.

Bill B.

[Moonlady]

I got the habbit of renaming APODS when I want to save them...this one is:

gemstones in the dark - seems like the galaxies are spread in the deep universe and they shine in different colors, beautiful!

[Rathkennamike]

Even in this picture it is possible to see that galaxies form on the interface of the frothy structure of space.
This make sense, as the energy spreads from multiple point events it is bound to interface much like the pressure ridges found in soap bubbles. At these pressure ridges is where matter will be most concentrated.

[icthioo3]

You seem to know a lot about the colors in this picture (XFD). At about 9 oclock there is a very faint "green" galaxy. There doesn't seem to be much green anywhere else in the picture. What causes the green color?

[Chris Peterson]

If we sent the Hubble telescope back in time and distance to the point where it has now collated these pictures, what would it see?

I believe exactly the same. Pictures from billions of years ago.

That's half right, but keep in mind that we are not looking at a surface here, but a volume. Photons captured by the camera were emitted over a long period of time, from billions of years ago to quite recently (because objects in the field range in distance from billions of light years to quite close). For the image as a whole, there is no point in either distance or time that describes it. You could pick any individual galaxy, and if you were near the point in space and time where these photons were produced, it would look as it does in the image. Other galaxies would look quite different, however, depending on their distance from that one galaxy. And of course, the edges of your observable universe would be different from ours, so there would be many things you could see from there that can't be seen from here, as well as things seen here that you couldn't see at all.

[Chris Peterson]

Even in this picture it is possible to see that galaxies form on the interface of the frothy structure of space.
This make sense, as the energy spreads from multiple point events it is bound to interface much like the pressure ridges found in soap bubbles. At these pressure ridges is where matter will be most concentrated.

I'm skeptical we can see anything like that looking at this small volume of space. I suspect it is an illusion of our visual processing system seeking to find lines and other patterns in an effectively random distribution that makes us see a degree of apparent structure.

[Ann]

You seem to know a lot about the colors in this picture (XFD). At about 9 oclock there is a very faint "green" galaxy. There doesn't seem to be much green anywhere else in the picture. What causes the green color?

I can think of the following possibilities:

1) This could be a galaxy which emits a lot of blue and ultraviolet light. This light would have been redshifted into the green part of the spectrum because the galaxy is far away. On the other hand, this is not entirely likely. The human eye isn't good at seeing multi-wavelength light as green. The reason for this is that our Sun can really be described as a green star, whose peak emission is in the green part of the spectrum. We certainly don't see the Sun as green. To my knowledge, "normal" galaxies which emit light of many wavelengths, like the Sun, practically never look green because of redshift.

2) This could possibly be a galaxy which emits a lot of blue light but far less ultraviolet light. It could be a galaxy that has undergone a strong burst of star formation and then suddenly stopped forming stars altogether. An example of such a galaxy is M90, except that M90 also has a large and bright yellow population. To be so green, the galaxy would have to be the product of a single burst of star formation, where the O and B-type stars are all gone, and the dominant stars are of spectral class A. I'm still not sure that the overall blue color of such a galaxy could be redshifted into such a pure green color as the hue we are seeing in the green galaxy of today's APOD.

3) Another possibility is that the green galaxy, whose hue might be described as yellow-green, is a so-called Green Pea galaxy. Their color has to do with star formation, and also, or so I think anyway, with the presence of a lot of blue-green OIII emission. I believe that is some respects these galaxies might be compared with OIII-bright planetary nebulae. Please note that the intrinsic blue-green color of these galaxies could be redshifted into a yellow-green hue.

Ann

[Chris Peterson]

You seem to know a lot about the colors in this picture (XFD). At about 9 oclock there is a very faint "green" galaxy. There doesn't seem to be much green anywhere else in the picture. What causes the green color?

The only possible answer with the available information is to say that this galaxy is bright in the 1.1-1.4 um wavelength range, and dim from 0.9-1.2 um and 1.4-1.7 um. In order to understand what this means physically would require knowing the redshift of the object, so the original emission bands could be isolated.

Sometimes when we see a very bright and unusual color in an image like this it may simply reflect an artifact, as well- a few pixels, for instance, that didn't get much signal from all the wavelength channels because of something like a dust shadow or cosmic ray hit.

[Boomer12k]

Even the proto-galaxies, should follow the "clumping" effect of dark matter. They are after all "at the beginning" of it all...Thus forming the strands of galaxies we see as "the structure of the Universe"...thus we would expect to see delineation in matter, the placement of matter, and concentrations of matter. They are not just "flung" randomly. They hold to a pattern, a string of galactic groups and clusters...with a few stragglers...this is shown in pictures of the Universe's structure...supposed to be dark matter behind the scenes, but to me it looks like an explosion of paint. As it expands, it globs and splays, and thins, and stretches, as the area grows....it "spaghetti-fies"...into a web of wonderment...

Today's APOD image too, must be a part of that...


http://terraquegira.blogspot.com/2007/0 ... verso.html


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[ddale51]

There is a much more informative picture of what they are really talking about...it is not so much the "foreground" galaxies...this page has a cut out view...

You can't even see that spot in the magnified APOD view...

http://www.news.com.au/technology/sci-t ... 5995240242


:---[===] *

But, in checking out the above link, this news item was posted in January 2011. Is today's APOD reporting this same photo almost 2 years later?

[owlice]

http://hubblesite.org/newscenter/archiv ... s/2012/37/

[Boomer12k]

There is a much more informative picture of what they are really talking about...it is not so much the "foreground" galaxies...this page has a cut out view...

You can't even see that spot in the magnified APOD view...

http://www.news.com.au/technology/sci-t ... 5995240242


:---[===] *

But, in checking out the above link, this news item was posted in January 2011. Is today's APOD reporting this same photo almost 2 years later?

Many APODs are repeated...also, it takes time for an article or a picture to be noticed. APOD does not seem to be a "news" outlet, so I don't expect to see todays or tomorrows astronomy news on it. Just AWESOME pictures.

:---[===] *

[APOD Fan]

What a truly amazing image. The endless possibilities. As a layman, I could scarcely credit my senses just trying to imagine what's out there.

[owlice]

September 25, 2012: Like photographers assembling a portfolio of best shots, astronomers have assembled a new, improved portrait of mankind's deepest-ever view of the universe. Called the eXtreme Deep Field, or XDF, the photo was assembled by combining 10 years of NASA Hubble Space Telescope photographs taken of a patch of sky at the center of the original Hubble Ultra Deep Field.

From the FIRST LINK in today's APOD! This one, right here: http://hubblesite.org/newscenter/archiv ... s/2012/37/ This particular image is NOT a repeat; it's a "new, improved portrait..." Released last month! Notice the date, in bold above so people will notice the date!

[bystander]

There is a much more informative picture of what they are really talking about...it is not so much the "foreground" galaxies...this page has a cut out view...

You can't even see that spot in the magnified APOD view...

http://www.news.com.au/technology/sci-t ... 5995240242

That image is only infrared and I'm guessing the cut out is only in the farthest infrared. It would have much less significance in the combined view of the XDF.

But, in checking out the above link, this news item was posted in January 2011. Is today's APOD reporting this same photo almost 2 years later?

September 25, 2012: Like photographers assembling a portfolio of best shots, astronomers have assembled a new, improved portrait of mankind's deepest-ever view of the universe. Called the eXtreme Deep Field, or XDF, the photo was assembled by combining 10 years of NASA Hubble Space Telescope photographs taken of a patch of sky at the center of the original Hubble Ultra Deep Field.

From the FIRST LINK in today's APOD! This one, right here: http://hubblesite.org/news/2012/37 This particular image is NOT a repeat; it's a "new, improved portrait..." Released last month! Notice the date, in bold above so people will notice the date!

http://asterisk.apod.com/viewtopic.php?t=29624

As owlice mentioned, today's image is a new release made from observations that includes HUDF and HUDF-IR data, along with new data.

Exposure Date(s): July 2002 to March 2012
Release Date: September 25, 2012

The image Boomer12k linked to is from an extended HUDF-IR - Hubble Site release: STScI-2011-05

Exposure Date(s): August 26, 2009 – September 14, 2010
Release Date: January 26, 2011

Exposure Date(s): August 26, 2009 - September 6, 2009
Release Date: December 8, 2009

Exposure Date(s): September 24, 2003 - January 16, 2004
Release Date: March 9, 2004

[Ann]

Thanks, bystander. So if I get this correctly, the galaxy that looked brightly green in this Extreme Deep Field was bright in filters F775W(I)+F814W(I)+F850LP(z), which if I get it correctly, means it primarily emitted photons corresponding to wavelengths between 775nm and 850nm. That's a pretty narrow range, less than 100 nm.

Ann

[bystander]

Thanks, bystander. So if I get this correctly, the galaxy that looked brightly green in this Extreme Deep Field was bright in filters F775W(I)+F814W(I)+F850LP(z), which if I get it correctly, means it primarily emitted photons corresponding to wavelengths between 775nm and 850nm. That's a pretty narrow range, less than 100 nm.

Looking at the WFC3 Filter Throughputs for those filters, I would put the range at 700nm-900nm, with substantially weaker signals at 450nm-700nm and 900nm-1700nm. As Chris has stated, without knowing the distance and redshift of the target, I'm not sure what more could be said about it.